I have a couple hundred acres of bush and at the back on one of them is a small stream and an opening where I do my shooting. I shot the sks prone on a mound of earth. No sand bags and with black flies and deer flies bugging me.
That's very good to know. I asked because the usual frame of reference is someone shooting a load that they worked up from a shooting bench, with some sort of rest or sandbags to steady the gun, and usually in more comfortable conditions than you described. That's what you're usually looking at when someone posts groups on this site.
Like I wrote, your groups looked comparable to what I'd get from a pretty stable sitting on the ground with shooting sticks position, so what you've achieved is pretty decent. If you had the means to sight in the rifle off of a bench, I suspect that your groups would still tighten up. Perhaps not so much as some better scoped or open sighted rifles, but still better than your posted groups.
I'm not someone who'd try to claim that the SKS is a tack-driver, but I think that much of their reputation for mediocre/poor accuracy comes from people who don't care to shoot too carefully when using their rifles.
For regular bush hunting applications, the SKS will pretty much do anything a .30.30 will do. Besides, the cheaper ammo for them means that you should easily be able to practice with all of the shooting postions and ranges that you'd use when hunting, which is the best prep.